The present invention relates to panel fasteners affixed to circuit boards and, in particular, to panel fasteners of the type having a molded cap composed of a material such as ABS Plastic. More specifically, it relates to panel fasteners of the type disclosed in U.S. patent application Ser. No. 09/739,689 entitled xe2x80x9cSnap-In Panel Fastenerxe2x80x9d which is herein incorporated by reference as though fully set forth.
There are cases in which panel fasteners of the hybrid type, that is fasteners in which the screw portion has a molded-on plastic cap for ease of manual operation, are required to be soldered to a printed circuit board. A problem arises, however, due to the soldering temperature required to affix the retainer portion of the panel fastener to the PCB because the soldering heat has an adverse effect on the materials used in the plastic portion of the panel fastener. This problem not only arises with regard to soldering to PCBs but may also arise in other situations where attachment of the retainer to a base panel requires elevated temperatures. There is therefore a need in the art to provide a hybrid-type panel fastener that may be soldered or applied to a base panel by heating without adversely affecting its plastic portion.
In order to meet this need in the art, the present invention has been devised in which the two main components of the panel fastener, the screw cap portion and the metal retainer portion, are assembled together after the retainer is soldered to the PCB and the retainer has cooled. The screw cap assembly is later attached to the soldered retainer by the snap action of its resilient parts. Since the screw cap is away from the heat during soldering the retainer, it cannot be adversely affected. Accordingly, the present invention provides a unique snap-together method provided by its structure which permits a low insertion force that can be accomplished by hand as well as automatic equipment so that the fastener can easily be installed onto a retainer after it has been soldered to a circuit board without damage to the PCB. Since the high force of assembly required by prior art hybrid-type panel fasteners would severely damage the PCB and also require expensive installation equipment and tooling, the low assembly force of the screw cap assembly to the retainer of the invention avoids these problems.
More specifically, the applicants have invented a two-piece panel fastener comprising a generally barrel-shaped metal retainer which holds a screw. The retainer has a chamfered top flange along its top edge, a circumferential bulge area along its outer surface approximately in the middle of its length, and a base at the bottom. Two circumferential valley regions of reduced diameter are located along the outer surface of the retainer. The first valley region is located between the chamfered top flange and the bulge area and the second is located between the bulge area and the base. The screw includes a threaded shaft and a plastic cap which has longitudinally-extending resilient fingers as means to engage the outer surface of the retainer to captivate the screw. The screw is captively held at either of two stable positions of retraction or extension where the fingers occupy either of the valley regions. The retainer is preferably rigidly affixed to a circuit board by soldering a base flange at the bottom of the retainer to the top surface of the panel. The shank extends axially downward from the flange and lies within a hole in the PCB during soldering. The threaded portion of the screw extends beyond the shank of the retainer when the screw is in the extended position.
The method of assembling the captive panel fastener to a printed circuit board comprises the steps of placing an axially-extending shank of a captive fastener retainer through a mounting hole in a printed circuit board, soldering the retainer to the printed circuit board, cooling the retainer, and then affixing a retractable screw assembly including a plastic screw cap to the retainer by snap attachment of the screw cap to an outside surface of the retainer.
In another embodiment, the panel fastener comprises a generally cylindrical retainer having a base flange at the bottom. An inward-facing flange is located at the top of a through-hole in the retainer, and includes a lead-in ramp at the top and a steep angle on an underside. The screw has a threaded shaft and a plastic cap rigidly affixed to its head. A deformable ring is located around the shaft of the screw at the top of a threaded region and has a relaxed diameter greater than the inside diameter of the retainer through-hole flange such that the ring engages an underside of the flange when the screw is retracted thereby captivating the screw.
The applicants have therefore devised a unique two-piece hybrid panel fastener with a structure and method of attachment which permits it to be used in solder-on applications to PCBs without damage to either the fastener or the PCB. Other objects and advantages of the present invention will become apparent to those of skill in the art from the following drawings and description of the preferred embodiment.